During early development Xenopus replicates its DNA nearly as fast as E. coli in log phase. Therefore, oocytes are an excellent source of proteins responsible for DNA repair and replication activity. We continued to characterize both DNA repair activity and single-strand to double-strand replication activity in Xenopus oocytes and our nuclear extracts. Pyrimidine dimers, (6,4) photoproducts and bulky chemical adducts undergo nearly complete repair, with no background synthesis on undamaged control DNA, in both microinjected oocytes and nuclear extracts. Unlike other extracts that repair <2% of the input damaged DNA, our extracts repair all of the damaged substrate and results in the extracts appear to accurately reflect events in living cells. Although the ss to ds replication activity is also very efficient both in oocytes and extracts, we demonstrated that surprisingly the presence of slight damage on a ss template completely suppresses the otherwise efficient replication reaction. This replication suppression may represent a new type of checkpoint for processing damage that either escaped G1 arrest or occurred after entry into S-phase.